Robust Cuts Over Time: Combatting the Spread of Invasive Species with Unreliable Biological Control (original) (raw)
Related papers
ECOLOGY: Biological Control of Invading Species-Risk and Reform
Science, 2000
Biological control (BC), the science and technology of controlling pests with natural enemies, has had several recent successes, including suppression in Africa of invading mealybug and whitefly pests of cassava by means of introduced wasps (1). Increasingly, BC is used to suppress weeds in natural areas, such as the ecosystems of South African Cape Fynbos, the Australian Kakadu National Park, and the Florida Everglades, U.S.A. (2). The Everglades BC projects include control of the Old World climbing fern Lygodium microphyllum (see the figure). Biological control is also contemplated against insects invading natural areas and even against invasive marine species (3). The invasive species L. microphyllum is shown here (light green) blanketing Everglades tree islands in Loxahatchee National Wildlife Refuge in southern Florida. The insets show the adult and larval stages of an Australian moth Cataclysta camptozonale now being evaluated as a potential biological control of the fern.
Current Opinion in Insect Science, 2014
Although records show that the loss of susceptibility of pests to biological control agents is an exceedingly rare event, there are certain behavioural and ecological settings that may well predispose to it. In general, these circumstances rarely converge. Such a critical combination of factors could possibly occur in agroecosystems based on incomplete transplants imported from elsewhere. It can be argued that such ecosystems lack the biodiversity required to confer biotic resistance to invasive species and this can result in spectacularly high and damaging pest densities. Through exactly the same mechanism, introduced control agents such as parasitoid wasps, similarly can prove to be very successful in producing persistently very high levels of parasitism of pests, leading to triumph. However, this feeling may be short-lived. When success is based on very high selection pressure on the host pest species this could have the potential to lead to the evolution of resistance to the control agent. This is particularly so should it coincide with factors such as a lack of pest host refugia, parasitoid parthenogenetic reproduction, versus pest sexual reproduction, as well as suppression based on a narrow range of natural enemies. In effect, the very thing that can lead to spectacular success can eventually become the basis for failure. For the purposes of illustration, these considerations are illustrated via what seems to be a developing cause for concern about biological control in New Zealand's pastures.
Can the control of invasive species be left to chance?
Natural Resources & Engineering, 2016
Invasive species are said to be a bigger threat to native biodiversity than pollution, harvest, and disease combined. In order to preserve native flora, fauna, and natural resources of regions, the effective control of invasive species is imperative. We consider a three-species predator-prey model, where the top predator, functions as an invasive species, with the ability to grow explosively to 'uncontrollable' levels in a finite time, if unchecked. We investigate the effect of random environmental forces, on such explosive growth. We find that environmental noise alone, cannot prevent explosive growth in invasive populations. We interpret these results as showing that invasive species can strongly adapt to a randomly changing environment. We provide supporting evidence of such phenomenon, from the ecological literature. Our results are applicable to a wide variety of natural resource management practices.
Limits and Potentialities of Eradication as a Tool for Addressing Biological Invasions
Eradication is the complete and permanent removal of all wild populations of an alien plant or animal species from a defined area, by means of a time-limited campaign.This measure is therefore different from control, i.e. the reduction of population density and abundance in order to keep damage at an acceptable level, and containment, aimed at limiting the spread of a species by containing its presence within defined geographical boundaries (Bomford and O’Brien 1995). Following this definition, also the removal of very few individuals is an eradication, if these have the potentialities of reproducing and establishing in the wild (i.e. this does not include the removal of single animal individuals but includes removal of seeds or plant propagules in the wild, or of a few pairs of animals). Eradication of unwanted alien species is an increasingly important tool for conservation of biological diversity. In fact, although the most effective way for mitigating the impacts caused by biological invasions is the prevention of new unwanted introductions, once prevention has failed and an alien species has invaded a new area, eradication is the best alternative, considering the costs and undesired effects related to permanent control or to a “do-nothing” policy.
Control and the management of a spreading invader
We consider the problem of management of an aquatic invader spreading in a lake system. We assume that each year the invader can be removed from a certain proportion of invaded lakes, which depends on the selected intensity of control. Control decisions are generated and compared for an optimally controlled system and for a static optimization across asymptotic steady states. Control close to eradication of the invasive species is always optimal for invasions with relatively high damages, low rates of density dependent spread and/or low chance of additional random introductions. Control to a highly invaded steady state is optimal for those invasions with low relative damages, high chances of random introduction and high levels of uncertainty in species location. In all other cases the optimal outcome depends upon initial conditions. Comparing the relative performance of the optimally controlled system and the static optimization demonstrates situations when the differences are small and when not. When invasions are acted upon in their later stages and across certain parameter combinations a static optimization provides a reasonable approximation of an optimally controlled system. The flip-side is that optimal policies directed at an invasion in its early stages tend to provide significantly savings. The savings vary across parameter combinations, yet in these situations little useful insight will be generated without consideration of a dynamically optimized system. ß
Simple rules to contain an invasive species with a complex life cycle and high dispersal capacity
Journal of Applied Ecology, 2012
1. Designing practical rules for controlling invasive species is a challenging task for managers, particularly when species are long-lived, have complex life cycles and high dispersal capacities. Previous findings derived from plant matrix population analyses suggest that effective control of long-lived invaders may be achieved by focusing on killing adult plants. However, the cost-effectiveness of managing different life stages has not been evaluated. 2. We illustrate the benefits of integrating matrix population models with decision theory to undertake this evaluation, using empirical data from the largest infestation of mesquite (Leguminosae: Prosopis spp) within Australia. We include in our model the mesquite life cycle, different dispersal rates and control actions that target individuals at different life stages with varying costs, depending on the intensity of control effort. We then use stochastic dynamic programming to derive costeffective control strategies that minimize the cost of controlling the core infestation locally below a density threshold and the future cost of control arising from infestation of adjacent areas via seed dispersal. 3. Through sensitivity analysis, we show that four robust management rules guide the allocation of resources between mesquite life stages for this infestation: (i) When there is no seed dispersal, no action is required until density of adults exceeds the control threshold and then only control of adults is needed; (ii) when there is seed dispersal, control strategy is dependent on knowledge of the density of adults and large juveniles (LJ) and broad categories of dispersal rates only; (iii) if density of adults is higher than density of LJ, controlling adults is most cost-effective; (iv) alternatively, if density of LJ is equal or higher than density of adults, management efforts should be spread between adults, large and to a lesser extent small juveniles, but never saplings. 4. Synthesis and applications. In this study, we show that simple rules can be found for managing invasive plants with complex life cycles and high dispersal rates when population models are combined with decision theory. In the case of our mesquite population, focussing effort on controlling adults is not always the most cost-effective way to meet our management objective.
A proposed unified framework to describe the management of biological invasions
Biological Invasions, 2020
Managing the impacts of invasive alien species (IAS) is a great societal challenge. A wide variety of terms have been used to describe the management of invasive alien species and the sequence in which they might be applied. This variety and lack of consistency creates uncertainty in the presentation and description of management in policy, science and practice. Here we expand on the existing description of the invasion process to develop an IAS management framework. We define the different forms of active management using a novel approach based on changes in species status, avoiding the need for stand-alone descriptions of management types, and provide a complete set of potential management activities. We propose a standardised set of management terminology as an emergent feature of this framework. We identified eight key forms of management: (1) pathway management, (2) interception, (3) limits to keeping, (4) secure keeping, (5) eradication, (6) complete reproductive removal, (7)